1. Field of Invention
The invention relates to integrated circuit devices, and more particularly, to fusible link devices in semiconductor integrated circuits in which the laser fuse is made in the poly-Si level, as opposed to the metal level, which can be placed in oxide.
2. The Prior Art
In general, today, integrated circuits are made with internal connections that are set during manufacturing; however, due to high development costs, lengthy lead times, and the high tooling costs of these circuits, the end user prefers circuits which can be programmed in the field. These circuits are typically referred to as programmable circuits since they usually contain programmable links.
Programmable links are electrical interconnects which are broken or created at selected electronic nodes by the end user after the integrated circuit device has been fabricated in order to activate or deactivate the selected electronic nodes.
As a case in point, programmable links are used widely in programmable read-only memory devices (PROMs). In this connection, it is pointed out that the most common form of programmable link is the fusible link. Upon obtaining a PROM device, typically it will consist of an X-Y lattice of conductors or semiconductors. The lattice comprises a cross-over point of a conducting link, which is referred to as a fusible link, that connects a transistor to this lattice network. To program the PROM, the fusible link is blown at selected nodes to create an open circuit. The combination of blown and unblown links constitutes a digital bit pattern of ones and zeros that constitute data which the user stores in the PROM.
Some of the key disadvantages of fusible link PROM systems is that, because of the nature of the conducting material in the link, high voltage and high current levels are usually needed during programming in order to complete blowing of the fusible link. Because the link is relatively high in conductance, it requires a considerable amount of power dissipation to blow it. Further, the size and shape of the fusible link must be exacting so that the link will function effectively as a conductor if it is not blown and be a completely open circuit if it is blown.
A second type of programmable link has also been utilized frequently. The second type of programmable link is referred to as an anti-fuse link, and enjoys considerable use in integrated circuit applications. In the anti-fuse link, instead of the programming mechanism causing an open circuit as is the case with fusible links, the programming mechanism creates a short circuit or low resistance link. The anti-fuse link consists of two conductor and/or semiconductor materials with a dielectric or insulating material between them. During programming, the insulating or dielectric material at selected points in between the conductive material is broken down by a predetermined applied voltage to electrically connect the conducting or semiconducting materials together.
A silicide agglomeration fuse device is disclosed in U.S. Pat. No. 5,708,291. The fusible link device is disposed on a semiconductor substrate and comprises:
a polysilicon layer having a first resistance;
a silicide layer formed on the polysilicon layer, the silicide layer having a second resistance lower than the first resistance, the silicide layer agglomerating to form an electrical discontinuity in response to a predetermined programming potential being applied across the silicide layer, such that the resistance of the fusible link device can be selectively increased and;
nine contacts electrically coupled to either end of the silicide layer for receiving the programming potential.
U.S. Pat. No. 5,969,404 disclose a fusible link device on a semiconductor substrate for providing discretionary electrical connections. The fusible link device has a first un-programmed resistance and includes a polysilicon layer and a silicide layer. The silicide layer is formed on the polysilicon layer, and agglomerates to form an electrical discontinuity in response to a predetermined programming potential being applied across the silicide layer, such that the resistance of the fusible link device can be selectively increased to a second programmed resistance.
A polysilicon fuse array structure for integrated circuits is disclosed in U.S. Pat. No. 5,536,968. The semiconductor structure comprises:
a first electrical conductor;
a second electrical conductor electrically separated from the first electrical conductor;
a polysilicon strip connecting the first and second electrical conductors and forming a fuse between the first and second electrical conductors, the polysilicon strip including a narrow middle section, whereby the fuse will be opened by a current which is passed from the first electrical conductor through the polysilicon strip into the second electrical conductor;
a first patterned signal layer, the first electrical conductor and the polysilicon strip residing in the first patterned signal layer; and
a second patterned signal layer electrically separated from the first patterned signal layer, the second electrical conductor residing in the second patterned signal layer.
U.S. Pat. No. 6,104,079 disclose closely pitched polysilicon fuses and a method for making the same. In the method for decreasing the pitch of polysilicon fuses tungsten barriers are formed adjacent to the fuse elements and the tungsten barriers are made compatible with the process to form a crack stop. The tungsten is stacked at the via level on top of the tungsten at the contact level in the crack stop, and the interlevel dielectric is used as a cover for the fuse. In this way, the tungsten fuse barrier process is made compatible with the polysilicon fuse crack stop process.
An electrically global fuse in a reduced co-sectional area is disclosed in U.S. Pat. No. 6,222,244 B1. The semiconductor fuse is positioned between conductors for connecting at least two wiring lines. The fuse comprises spacers positioned on adjacent one's of the conductors, and the fuse element is positioned between the spacers and connected to the wiring lines. A space between the conductors comprises the first width comprising a smallest possible photolithographic width and the fuse element has a second width smaller than the first width. This fuse protects the semiconductor device from excessive voltage and/or current or selectively and permanently connect/disconnect semiconductor devices from one another.
U.S. Pat. No. 5,266,829 disclose an electrically programmable low-impedance, anti-fuse element. It consists of a capacitor-like structure having a first electrode and a second electrode with a dielectric layer in between, characterized by a high impedance and very low leakage current before programming and a low-resistance after programming. A plurality of these anti-fuses is disposed in a semiconductor integrated circuit, and maybe selectively blown to create low impedance interconnects at selected locations within the integrated circuit. The anti-fuses may be blown either before or after packaging of the integrated circuit die.
U.S. Pat. No. 5,882,998 disclose a low power programmable fuse structure and method of making the same.
The method comprises:
providing a substrate having a filed oxide region;
forming a mask over the doped polysilicon strip such that a window exposing the doped polysilicon strip is defined at about the center of the doped polysilicon strip;
applying an increased implant dose over the mask and the exposed doped polysilicon strip lying within the window to produce an increased dopant concentration region in the doped polysilicon strip, the increased implant dose being between about 3.1015 cm−2 and about 6×1015 atoms cm−2; and
forming a silicide metal over the doped polysilicon strip such that a thinner layer of the silicide metal is formed over the increased dopant concentration region and a thicker layer of the silicide metal is formed over other regions of the doped polysilicon strip.
There is a need in the art of utilizing programmable fuses in integrated circuits to reduce the damage to SILK by other than the current method of using fuses in the final metal level which may be placed in oxide, and wherein some damage to the structure still results.
There is a further need in the art of providing programmable fuse links for use in integrated circuits to alleviate physical damage to the structure, as is typically the case when the fuses are electrically programmed.
There is a further need in the art of providing programmable fuses for use in integrated circuits to be able to utilize less energy when compared to ablation or melting, and to reduce the pitch and damage to nearby structures.
Finally, there is a need in the art of providing programmable fuses for use in integrated circuits to eliminate refractory metals that are normally needed as liners for poly-Si lines, to be able to use shorter wavelengths, and thereby tighter focal spots that lead to reduced pitch, but which also lends itself to being electrically programmed (and thereby provide the improved flexibility of affecting programming with either optical energy or electrical energy).